The purpose of this project is to delineate the mechanisms involved in regulating immune responses in filarial and nonfilarial disease states. Immunoregulatory studies have examined the phenomenon of antigen-specific anergy in microfilaremic patients by showing this anergy to be a result of the production of the antiproliferative cytokine, IL-10. Filter immunoplaque assays for the major cytokines have been developed and used to demonstrate that in helminth infections of humans there is an expansion of Th2 CD4+ cells. The phenotypic characterization of these Th2 CD4+ cells has shown them to be CD45RO+ HLA-DR+ CD27-; a novel method for intracellular staining for cytokines has been used to assess further the frequency of these cells. Similarly, new ways of assessing eosinophil activation have also been developed.